1. Field of the Invention
The present invention relates to a wireless local area network (WLAN), and more particularly, to a method and apparatus for Dynamic Station Enablement (DSE) procedure in a wireless local area network system.
2. Discussion of the Related Art
The standard for a Wireless Local Area Network (WLAN) technology is established by IEEE 802.11 standard association. IEEE 802.11a/b among IEEE 802.11 standards provides 11 Mbps (IEEE 802.11b) or 54 Mbps (IEEE 802.11a) transmission efficiency using unlicensed band on 2.4. GHz or 5 GHz frequency band. IEEE 802.11g, adapting OFDM (Orthogonal Frequency Divisional Multiplexing) technology, provides 54 Mbps transmission efficiency. And, IEEE 802.11n, adapting MIMO-OFDM technology, provides 300 Mbps transmission efficiency for 4 spatial streams. IEEE 802.11n provides 40 MHz channel bandwidth, and in this case it provides up to 600 Mbps transmission efficiency.
Now, a standard for regulating the WLAN operation in TV White Space is under establishment, as IEEE 802.11af.
TV Whitespace includes channels allocated to broadcast TV, which are permitted to be used by cognitive radio device, and includes 512-698 MHz spectrum. The spectrum not used by a licensed device (hereinafter, can be called as ‘White Space’) can be used by an unlicensed device. Here, ‘licensed device’ means a device of the user permitted in this frequency band, and can be differently called as ‘primary user’, or ‘incumbent user’ Hereinafter, the term of ‘incumbent user’ can be collectively used for these terms.
The unlicensed device, which wishes to use the TV White Space (TVWS), shall acquire information for available channel list at its location. Hereinafter, the unlicensed device operating in the TVWS using MAC (Medium Access Control) and PHY (Physical) operation according to IEEE 802.11 can be called as TVWS terminal.
Unlicensed device should provide a protection mechanism for the incumbent user. That is, the unlicensed device should stop using a specific channel, when an incumbent user, such as wireless microphone, is using that specific channel. For this purpose, spectrum sensing mechanism is required. Spectrum sensing mechanism comprises Energy Detection scheme, Feature Detection scheme, etc. By using this mechanism, unlicensed device determines that the channel is used by an incumbent user, when the strength of the primary signal is greater than a predetermined level, or when DTV (Digital Television) Preamble is detected. And, the unlicensed device (station or Access Point) shall lower its transmission power, when it is detected that the neighboring channel, next to the channel used by the unclosed device, is used by the incumbent user.
When unlicensed devices operate on licensed bandwidth such as TVWS, the unlicensed devices are classified as enabling stations and dependent stations.
An enabling station is a station which can enable a dependent station. The enabling station can transmit a signal without receiving an enabling signal and initiate network. On the other hand, a dependent station can transmits a signal only when receiving an enabling signal and operate under control of an enabling station. However, when the dependent station receives enabling signal from a dependent AP, it cannot perform enablement because it does not know an address of an enabling station.